This invention concerns a multi-color recording device that records multiple colors by using a plurality of heat sensitive recording heads and thermally transferring inks of different hues on a single recording paper sheet at respective positions, and more specifically, it relates to a multi-color recording device capable of preventing positional displacement on the recording paper sheet of the images recorded at each of the heat sensitive recording heads.
In a heat transfer recording device, ink donor sheets each coated with heat fusible solid ink on one surface of a substrate are used, and heat is selectively supplied from thermal heads to the ink donor sheets in accordance with picture information. Then, the ink thus fused is transferred to the recording paper sheets for recording of information. Accordingly, multi-color recording can be carried out by preparing a plurality of ink donor sheets which are each coated with solid inks of different hues, and by successively conducting heat transfer recording on one recording paper sheet with these ink donor sheets.
FIG. 1 shows a conventional multi-color recording device based on the foregoing principle. In this device, a first ink donor sheet 1 is supplied from a first feed roll 2 and then is taken up by way of a guide roll 3, a thermal head 4 and another guide roll 5 onto a take-up roll 6. A second ink donor sheet 7 is supplied from a second feed roll 8 and is thereafter taken-up by way of a guide roll 9, thermal head 10 and another guide roll 11 onto a take-up roll 12 in the same manner. In a first recording region 13 in which the first thermal head 4 and the first ink donor sheet 1 are in contact with each other, a first pressure roll 15 rotated in the direction of an arrow 14 upon recording is contacted and, when a recording paper sheet (ordinary paper) 16 advances into the first recording region 13, the first pressure roll 15 urges the sheet under pressure against the ink surface of the ink donor sheet 1 and conveys the recording paper in the direction of an arrow 17 at a speed equal to the circumferential speed of the pressure roll 15. In this case, the first thermal head 4 selectively causes its heat generation members to generate heat based on red color picture information, for example, to thereby transfer the red ink from the first ink donor sheet 1 onto the recording paper sheet 16.
The recording paper sheet 16 sent out from the first pressure roll 15 then advances by way of a guide 18 into a second recoridng region 19 where the second ink donor sheet 7 and the second thermal head 10 are in contact with each other. In the second recording region 19, a second pressure roll 21 rotated in the direction of an arrow 20 upon recording is contacted and, when the recording paper sheet 16 advances into the second recording region 13, the second pressure roll 21 contacts the recording paper under pressure against the ink surface of the second ink donor sheet 7 and sents the sheet forwardly. In this case, the second thermal head 10 causes its heat generation members to generate heat selectively based on the black color picture information, for example, to thereby transfer the black ink from the second ink donor sheet onto the recording paper sheet 16.
In this way, in the foregoing multi-color recording device, picture information for red color and black color are recorded in the two recording regions 13, 19. However, if the distance between the two recording regions 13, 19 is large, the delay time between the supply of the picture signal to the first thermal head 4 and the supply of the picture signal for the same position of the original to the second thermal head 10 has to be increased, which requires a memory of excessively large capacity. Accordingly, the distance between a plurality of recording regions has usually been set as short as possible in the conventional multi-color recording device.
A problem with this, however, is that one recording paper sheet is not always transported by only one pressure roll but it may sometimes be engaged and transported simultaneously by a plurality of pressure rolls. Rubber rolls used for the pressure rolls usually have diameters which vary by several percent. Accordingly, when a recording paper sheet is transported by a plurality of pressure rolls simultaneousely, the circumferential speeds on each of the pressure rolls may differ slightly and, as a result, the transportation speed for the recording paper sheet becomes unstable and color displacement is caused.